Process conditions change monitoring systems that use electron beams, and related monitoring methods

ABSTRACT

In order to accurately monitor changes in exposure conditions (changes in exposure level and focus) at a product wafer level during lithography, changes in exposure conditions can be calculated by acquiring electron beam images of a first pattern portion and a second pattern portion different from one another in terms of the tendency of the changes in dimensional characteristic quantities against the changes in exposure conditions, then calculating the respective dimensional characteristic quantities of the first pattern portion and the second pattern portion, and applying these dimensional characteristic quantities to the models which logically link the exposure conditions and the dimensional characteristic quantities. Hereby, it is possible to supply the process conditions change monitoring systems and methods that enable output of accurate changes in exposure level and focus.

BACKGROUND OF THE INVENTION

The present invention relates to the systems and methods in which,during lithography, whether pattern exposure to the resist film on awafer has been provided under the appropriate exposure conditions by useof electron beam images of the resist patterns. The invention relatesparticularly to the technology for controlling such an exposure processand maintaining the appropriate exposure conditions.

The flow of conventional lithography is described below.

The formation of a resist pattern is accomplished by coating asemiconductor wafer or a similar substrate with a resist (photosensitivematerial) to the required thickness, then exposing a mask pattern tolight using an exposure unit, and conducting a developing process. Theresist pattern that has thus been formed is dimensionally checked usinga scanning-type electronic microscope provided with a length measuringfunction (this microscope is called “length-measuring SEM or CD-SEM”).An example of processing with conventional length-measuring SEM isdescribed below. First after an electron beam image of the area whichincludes the section requiring stringent dimensional accuracy has beenacquired in process 1, dimensions are measured in process 2, thenwhether the dimensions satisfy reference values is judged in process 3,and if the reference values are not satisfied, the exposure level of theexposure unit is corrected in process 4 (the amount of correction of theexposure level is represented as ΔE). For example, in the case of apositive type of resist, if the resist size is too large, the exposurelevel is increased, and if the resist width is too small, the exposurelevel is reduced. It is not rare that the amount of correction of theexposure level is determined in accordance with the experience andworking knowledge of the operator.

FIG. 17 represents the relationship between a resist pattern and anafter-etching film pattern (data source: “Handbook of Electronic BeamTesting”, p. 255, a research document cited at the 98th Study Session ofthe 132nd Committee on the Application of Charged Beams to Industries,held under the auspices of the Japan Society for the Promotion ofScience). Given the same etching conditions, there is a relationship ofinvariableness between the shape of the resist pattern and that of thefilm pattern. To obtain a film pattern of the required shape, therefore,the resist pattern also needs to have the required shape. For example,during the comment of new processes, “conditions establishingoperations” for identifying the focus and exposure level at which therequired resist pattern shape can be obtained are performed by, aftercreating a wafer on which a pattern has been printed by changing thefocus and the exposure level with each shot (unit of exposure) [anexample of a wafer is shown in FIG. 18; such a wafer is usually calledthe focus exposure matrix (FEM)], measuring the dimensions of the resistpattern for each shot, then cutting the wafer, and examining itscross-sectional shape. A system for supporting the conditionsestablishing operations is set forth in Japanese Application PatentLaid-Open Publication No.Hei 11-288879. These operations are performedto determine the exposure level (E0) and focus value (F0) at whichgreater margins can be obtained, and the product wafer undergoesexposure based on the corresponding conditions. However, changes in thephotosensitivity of the resist, changes in the thickness of thereflection preventive film under the resist, drifts in the varioussensors of the exposure unit, and various other changes in processconditions, may prevent the required resist pattern shape from beingobtained under the E0 and F0 conditions that have been determined duringthe conditions establishingoperations. Dimensionalmeasurement (process2) described above takes place to detect these changes in processconditions, and the prior art described above is intended to compensatefor changes in resist shape, caused by changes in process conditions,through correcting the exposure level.

SUMMARY OF THE INVENTION

Under the prior art, the line width and other dimension values areexamined using length-measuring SEM to detect changes in processconditions and undertake corrective measures, and if the dimensionvalues do not satisfy reference values, the exposure level is corrected.The prior art, however, poses the following three problems:

The first problem is that changes in process conditions, not associatedwith any changes in the dimension values, more specifically, changes inthe focus value during exposure cannot be detected. The resist has anapproximately trapezoidal cross-sectional shape. Since inclined portionsare greater than flat portions in terms of secondary electron signalintensity, the signal waveform peaks at the portion corresponding to theedge of the trapezoid as shown in FIG. 19(a). An example of dimensionalmeasurement with length-measuring SEM is described below. As shown inFIG. 19(b), a straight line is drawn along both the outer portion andbase portion of the peak, then the crossing point of the two lines isderived, and after the same has also been performed on the other side,the distance between the two crossing points is taken as the line width.FIG. 20 is a graph on which the line width was plotted for each exposurelevel (from “e0” to “e8”) with the focus value plotted along thehorizontal axis in order to represent how the line width would changewhen the exposure level and the focus value changed. The magnitude ofthe exposure level increases in the order from “e0” to “e8”, and thereis the relationship that the line width decreases with increases in theexposure level (this relationship applies to a positive resist, and theopposite relationship is established for a negative resist). Changes inthe exposure level can therefore be detected by examining the linewidth. However, as is obvious from the graph, changes in the line widthare not too significant with respect to those of the focus value, andnear the appropriate exposure level of “e4”, in particular, even if thefocus value changes, the line width suffers almost no changes. Changesin the focus value, therefore, cannot be detected by examining the linewidth. On the other hand, even if the line width does not change, whenthe focus value changes, the cross-sectional shape of the resist willchange as shown in FIG. 20(b). Since, as described earlier in thisdocument, changes in the cross-sectional shape also affects the shape ofthe film pattern existing after etching, the use of the prior art whichdoes not enable changes in the focus value to be detected is likely tocreate large quantities of defects in the shape of the film patternexisting after etching.

The second problem is that deviations in focus value cannot, of course,be accommodated by merely correcting the exposure level only. Forexample, for situation A shown in FIG. 20(a), since the line width isgreater than its normal value, the exposure level will be increasedaccording to line width measurement results. However, since thedeviation in focus value must be corrected, situation B shown in FIG.20(b) will only result and the cross-sectional shape of the resist willnot return to normal. Consequently, defects in the shape of the filmpattern existing after etching are likely to be created in greatquantities in this case as well.

The third problem is that such quantitative information on processconditions changes that is required for the maintenance of a normalexposure process cannot be obtained with the above-described prior art.The tolerances for the exposure level and focus value are being narrowedvery significantly with the decreases in pattern rule in recent years.For example, for a semiconductor pattern whose design rule is 180 nm,the rate of change of pattern size is required to be controlled below10%, and to implement this, it is necessary to acquire information thatquantitatively represents changes in process conditions, that is to say,to obtain accurate data on what degree of deviation in the exposurelevel in terms of milli-joules and on what degree of deviation in thefocus value in terms of microns. In the case of the above-describedprior art, no deviations in the focus value can be detected, and itcannot be said that deviations in the exposure level are detectedaccurately, either. The reason is that in general, the line widthchanges with the focus value as well. The maintenance of a normalexposure process, therefore, cannot be anticipated with theabove-described prior art.

The object of the present invention is to supply the means that enablesthe detection of changes in focus value, particularly to supply theprocess conditions change monitoring systems and methods that enable thedetection not only of changes in exposure level, but also of changes infocus value, and output of accurate changes in both exposure level andfocus value.

In order to fulfill the object described above, the present inventionenables the below-described process conditions change monitoring systemand method to be constructed on length-measuring SEM.

In the present invention, a means of calculating the dimensionalcharacteristic quantities of resist patterns, including the edge widthsand pattern widths thereof, from the electron beam images that have beenacquired using length-measuring SEM, and a means of saving the modelsfor establishing logical linking between exposure conditions anddimensional characteristic quantities are provided and changes in theexposure conditions can be calculated by acquiring respective electronbeam images of a first pattern portion and a second pattern portiondifferent from one another in the tendency of the changes in dimensionalcharacteristic quantities against changes in the exposure conditions,then calculating the respective dimensional characteristic quantities ofthe first pattern portion and the second pattern portion, and applyingthese dimensional characteristic quantities to the models whichestablish logical linking between exposure conditions and dimensionalcharacteristic quantities.

Also, in the present invention, the first pattern portion has a patternconstructed so that the deviation of the focus value in its plusdirection increases the corresponding edge width, and the second patternportion has a pattern constructed so that the deviation of the focusvalue in its minus direction increases the corresponding edge width.

In addition, in the present invention, the above-described first patternportion uses a masked pattern and the above-described second patternportion uses a non-masked pattern.

Furthermore, in the present invention, different places in one image areused as the first pattern portion and the second pattern portion so thatthroughput does not decrease.

Furthermore, in the present invention, the relationship between changesin the edge width(s) and focus value(s) of the first and/or secondpattern, and the relationship between changes in the pattern width(s)and exposure level(s) of the first and/or second pattern, are storedinto memory as relational expressions, and these relational expressionsare used as the models for establishing logical linking between exposureconditions and dimensional characteristic quantities.

Furthermore, the present invention supplies a function thatautomatically calculates process window data from the relationshipbetween deviations in edge width and focus and from the relationshipbetween pattern width and exposure energy level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is process diagram of the lithography which uses the processconditions change monitoring system pertaining to the first preferredmode of embodiment.

FIG. 2 is a total block diagram of the CD-SEM pertaining to the firstpreferred mode of embodiment.

FIG. 3 is a diagram showing the creation sequence for a model whichlogically links exposure conditions and dimensional characteristicquantities.

FIGS. 4(a) through 4(c) are diagrams showing an example of patternssuitable for process conditions change monitoring.

FIGS. 5(a) through 5(c) are cross-sectional views showing an example ofpatterns suitable for process conditions change monitoring.

FIGS. 6(a) and 6(b) are graphs showing changes in edge width againstfocus.

FIGS. 7(a) and 7(b) are other graphs showing changes in edge widthagainst focus.

FIG. 8 is an explanatory diagram of the model representing therelationship between edge width and focus.

FIGS. 9(a) and 9(b) are diagrams showing the acquisition of the creationsequences for the models which establish logical linking betweenexposure conditions and dimensional characteristic quantities.

FIG. 10 is a diagram of the process conditions change monitoring systempertaining to the second preferred mode of embodiment.

FIG. 11 is a diagram showing another embodiment of a model whichlogically links exposure conditions and dimensional characteristicquantities.

FIGS. 12(a) and 12(b) are diagrams of the process conditions changemonitoring system pertaining to the third preferred mode of embodiment.

FIGS. 13(a) and 13(b) are diagrams showing a second example of patternssuitable for process conditions change monitoring.

FIG. 14 is a diagram showing the measuring method in the second exampleof patterns suitable for process conditions change monitoring.

FIGS. 15(a) and 15(b) are diagrams showing a third example of patternssuitable for process conditions change monitoring.

FIGS. 16(a) and 16(b) are diagrams showing the measuring method in thethird example of patterns suitable for process conditions changemonitoring.

FIG. 17 is an epitomic diagram representing the relationship between theresist pattern and film pattern existing before and after etching.

FIG. 18 is a view showing an example of a conditions establishing wafer.

FIGS. 19(a) and 19(b) are epitomic diagrams representing therelationship between the cross-sectional shape of a resist pattern andthe level of a secondary electron signal.

FIGS. 20(a) and 20(b) are graphs showing the relationship betweenexposure level, focus, and line width.

FIG. 21 is a focus value definition diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The first preferred mode of embodiment of the present invention isdescribed below using drawings.

(1) Total Flow of the First Preferred Mode of Embodiment

FIG. 1 relates to a first embodiment of the present invention and is aconceptual diagram of lithographic processes provided with a processconditions change monitoring system which has been constructed onCD-SEM. Portion 10 enclosed by a broken line in the figure denotes theflow of a product wafer in a semiconductor substrate manufacturingsystem, and the arrow indicates that processing advances in order fromthe left to the right. Also, portion 20 enclosed by a solid line denotesthe flow of processing by the process conditions change monitoringsystem constructed on CD-SEM, and the arrow indicates that processingadvances in order from top to bottom.

Changes in process conditions can be monitored in the conventionaltiming of dimensional checking. After an electron beam image of the areaincluding the first pattern portion and second pattern portion describedlater in this document has been acquired in process 11, line width LW1and edge width EW1 are calculated as the dimensional characteristicquantities of the first pattern portion in process 12, and edge widthEW2 is calculated as the dimensional characteristic quantity of thesecond pattern portion in process 13. After this, the calculation offocal deviation value ΔF is accomplished in process 14 by applying, toEW1 and EW2, the model for establishing logical linking between edgewidth and focal deviations, and the calculation of exposure level errorΔE is accomplished in process 15 by applying, to LW1, the model forestablishing logical linking between pattern width and exposure level.And in process 16, the results are fed back into the exposure conditionsfor exposure 17. Development 18 plates place under newly establishedexposure conditions, and after electron beam image re-acquisition 11,etching 19 and other processes are performed under newly establishedexposure conditions. Hereby, a new semiconductor substrate manufacturingsystem is supplied. In the present invention, if any deviations from theoptimal focus or exposure level values are detected (even within theprocess window data range), since the deviations will be detected andfed back into the exposure conditions, the normal status of the exposureprocess can be maintained. One of the greatest features of the presentinvention exists in that slight deviations in focus and in exposurelevel can be calculated accurately. Further details of the firstembodiment of the invention are described below.

(2) Configuration of the CD-SEM

First, the CD-SEM used for the process conditions change monitoringsystem pertaining to the present invention is described below. FIG. 2 isa block diagram showing the configuration of the CD-SEM. This figureshows an electron optical system 200. In FIG. 2, a primary electron beam202 from an electron gun 201 is emitted so as to pass through a beamdeflector 204, an ExB deflector 205, and an objective lens 206, andcondense on a wafer 100 (including a liquid-crystal substrate) placed ona stage 101. After the electron beam has been emitted, a secondaryelectron is emitted from wafer 100, a sample. The secondary electronthat has been emitted from wafer 100 is deflected by ExB deflector 205and detected by a secondary electron detector 207. A two-dimensionalelectron beam image is obtained by detecting the electron stemming fromthe sample in synchronization with either the two-dimensional scanningof the electron beam by deflector 204 or the X-axial repetitiousscanning of the electron beam by deflector 204, and with the Y-axialcontinuous movement of the wafer by stage 101. The signal that has beendetected by secondary electron detector 207 is converted into a digitalsignal by an A/D converter 208, from which the signal is then sent to animage processing section 300. Image processing section 300 has an imagememory medium 303 for temporary storage of digital images, and a CPU 304for calculating dimensional characteristic quantities from the imageswithin the image memory. The image processing section also has a memorymedium 301 which contains the models for establishing logical linkingbetween the exposure conditions and dimensional characteristicquantities that have been examined beforehand. A display unit 302 isconnected to image processing section 300 so that the necessaryequipment operations, detection results confirmation, and others can beimplemented via a graphical user interface (hereinafter referred to asthe GUI).

(3) Method of Model Construction

Next, the method of constructing the models to be used in processes 14and 15 of FIG. 1 is described below. The flow of model construction isshown in FIG. 3. In this embodiment, prior to product wafer loading, themodels are constructed using an FEM wafer.

After FEM wafer loading as process 2021, the wafer is aligned as process2022 and control is moved to the first measuring position as process2023.

In process 2024, an electron beam image of the area including a firstpattern portion and a second pattern portion is acquired. A maskedpattern with critical dimensions (the most stringent dimensions requiredwith respect to accuracy), and a non-masked pattern with criticaldimensions are suitable as the first pattern portion and the secondpattern portion, respectively. An example of patterns is shown in FIG.4. In this example, both a second pattern portion (a linear maskedpattern) and a first pattern portion (the leading end of a linearnon-masked pattern) are included. FIG. 4(a) shows an image processingsection 30 in a binary mask pattern image format, wherein white andblack denote a transmitting portion and a shielding portion,respectively, and a positive-type resist is assumed. FIG. 4(b) shows theimage of an after-development pattern. When an electron beam image ofthe section corresponding to the portion enclosed in a box in FIG. 4(a)is acquired, an image that represents bright edge portions and dark flatportions as shown in FIG. 4(c), will be obtained. The cross-sectionalshapes of sections A-B and C-D are shown in FIGS. 5(a) and 5(b),respectively. As shown in FIG. 5(a), for the film pattern having the A-Bcross section, the line width LW1 and edge width EW1 of the firstpattern portion are detected, and as shown in FIG. 5(b), for the filmpattern having the C-D cross section, edge width EW2 of the secondpattern portion is detected. The top edge of the first pattern portionassumes roundness with a plus focus value, and edge width EW1 isextended. At this time, the edge portion of the second pattern is almostthe same as formed with the best focus value. Also, for a minus focusvalue, the opposite is detected and although the edge portion of thefirst pattern is almost the same as formed with the best focus value,the bottom edge of the second pattern portion assumes roundness and edgewidth EW2 is extended. As can be seen hereby, the way the patternsuffers changes with changes in focus value differs between the firstpattern and the second pattern. Attaching attention to both the firstpattern and the second pattern enables one to estimate to what extentand in which direction the focus value deviates from the best focusvalue. Changes in process conditions can be estimated more accurately byinserting the monitoring-dedicated pattern including the first andsecond patterns into the wafer.

After acquired images have been saved as process 2025, the line widthLW1 and edge width EW1 of the first pattern portion are calculated andsaved as process 2026. Following this process, process 27 takes place tocalculate and save edge width EW2 of the second pattern portion. Theline width can be calculated in such manner as shown in FIG. 19(b),whereas the edge width can be calculated by measuring, as shown in FIG.5(c), the clearance between crossing point P1 of the lines drawn alongthe outer portion and base portion of the peak, and crossing point P2 ofthe lines drawn along the inner portion and base portion of the peak.Whether the particular position is the last measuring position is judgedas process 2028, and if not so, control is moved to the next measuringposition as process 2029; if the position is the last measuringposition, control is moved to process 2030.

In process 2030, after processes 2024 to 2027 have been performed on allmeasuring positions on FEM, the optimal exposure level is determinedfrom measurement results relating to line widths LW1 of all positions.In this phase, such a graph as shown in FIG. 20(a) is displayed in theGUI window and the exposure level at which the required line width hasbeen obtained is determined automatically or at the discretion of theoperator. In FEM, area 1001 of FIG. 9(a) is determined.

In process 2031, the relationship between focus and edge width isderived from the edge widths EW1 and EW2 measured in the vicinity of theoptimal exposure level (in FEM, area 1002 of FIG. 9(a)) that has havebeen determined as described above. The vicinity of the optimal exposurelevel means, for example, the range of the optimal exposure level ±2 mJ.As described earlier, EW1 is the edge width of the linear maskedpattern, and EW2 is the edge width at the leading end of the linearnon-masked pattern. The inventors' test results on the relationshipbetween these edge widths and focus are shown in FIG. 6. FIG. 6(a) showstest results on EW1, and FIG. 6(b) shows test results on EW2. In bothcases, the edge widths in the focus range from −0.5 to +0.5 microns forexposure levels of 32 mJ, 33 mJ, 34 mJ, 35 mJ, and 36 mJ (optimalexposure level: 34 mJ) are plotted along the vertical axis, and thefocus values are plotted along the horizontal axis. As shown in thefigure, a significant difference exists between EW1 test results and EW2test results. That is to say, the former significantly changes in theminus direction and does not significantly change in the plus direction,whereas the latter significantly changes in the plus direction and doesnot significantly change in the minus direction. In process 2031 of FIG.5, a model for calculating the focus value from two edge width values iscreated by use of the difference in behavior between EW1 and EW2. Inother words, this process is performed to supply a model saving means(unit). An example of such a model is shown in FIG. 7. In this figure,the numeral 1 is assigned to the expression of EW1−EW2 (FIG. 7(a)) at 32mJ, 33 mJ, 34 mJ, 35 mJ, and 36 mJ, and the results are taken as amodel.

[Numerical Expression 1] $\begin{matrix}{f = {{c\quad \frac{e^{a\quad {({x - b})}} - e^{{- a}\quad {({x - b})}}}{e^{a\quad {({x - b})}} + e^{{- a}\quad {({x - b})}}}} + d}} & {{Numerical}\quad {expression}\quad 1}\end{matrix}$

where x=EW1−EW2.

The numeral 1 is for calculating focus value “f” from “x =EW1−EW2”, andparameters “a”, “b”, “c”, and “d” in the expression are determined byassigning the numeral 1 to FIG. 7(a) and using a method such as theleast squares method. Although the parameters are calculatedautomatically, such graphs as shown in FIGS. 7(a) and 7(b) are displayedin the GUI window and the operator can confirm whether the model isappropriate. If the model is judged to be inappropriate, the operatorcan modify the model by, for example, deforming the curve of FIG. 7(a)using a tool such as a pointing device. After the model has beenmodified, a relational expression in which the parameters have beenmodified to “a′”, “b′”, “c′”, and “d′”, is establishes or the modelitself is saved as a look-up table.

In process 2032, the focus value range where the rate of change of theedge width with respect to focus is maintained at or below a fixed value(for example, within ±2.0 microns) is determined and this range isdefined as focus margins (focal deviation tolerances). Morespecifically, an absolute value is obtained by differentiating thenumeral 1 by “x”, and the range in which the absolute value ismaintained at or below a separately determined threshold value is takenas focus margins. These margins are equivalent to the focal depths ofthe exposure unit in the corresponding pattern dimensions. FIG. 9 is adiagram showing the acquisition of the creation sequences for the modelswhich establish logical linking between exposure conditions anddimensional characteristic quantities. FIG. 9(a) is a diagram showingthe relationship between exposure level and focus value, and FIG. 9(b)is a diagram showing the tolerance for the focus value. In FEM, area1003 in FIG. 9(b) corresponds to the focus margins.

In process 2033, the relationship between exposure level and line widthis derived from the measurement results relating to line width LW1within the focus margins which have been determined as described above.The inventors' test results on the relationship between line width LW1and exposure level are shown in FIG. 8. FIG. 8 shows the results thatwere obtained when the line widths at various exposure levels wereplotted with each exposure level taken along the horizontal axis in thefocus range from −0.2 to +0.2 microns (focus margins from −0.2 to +0.2microns). As shown in the figure, there is the relationship that linewidth linearly decreases with increases in exposure level. In thisfigure, the numeral 2 is assigned to the line widths in the range from−2 to +0.2 microns, and the results are taken as a model.

[Numerical Expression 2]

e=−hx+g  Numerical expression 2

where x=LW1.

The numeral 2 is for calculating exposure level “e” from “x=LW1”, andparameters “h” and “g” in the expression are determined by assigning thenumeral 2 to FIG. 8 and using a method such as the least squares method.The method of operator intervention via the GUI window is the same asfor process 2032.

In process 2034, the exposure level range in which the line width stayswithin its fixed value ±α is derived from the numeral 2 and thisexposure level range is determined as exposure level margins (exposurelevel error tolerance). α is a separately determined threshold value,which is usually set to about 10% of the line width. In FEM, area 1004(shaded portion) in FIG. 9(b) corresponds to the threshold value, and inprocess 2035, the center of this area is registered as the optimalexposure level E0 and the optimal focus value F0.

(4) Monitoring of Changes in Process Conditions

Next, attention is returned to FIG. 1 and the method of monitoringchanges in process conditions is described below.

First, the optimal exposure level E0 and the optimal focus value F0 areset as the exposure conditions for the commencement of product waferprocessing. After this, process conditions change monitoring shown inFIG. 1 occurs in synchronization with the dimensional measurement of theproduct wafer. Processing up to acquiring an electron beam image of thearea including the first and second pattern portions, and calculatingLW1 and EW1 as the dimensional characteristic quantities of the firstpattern portion and EW2 as the dimensional characteristic quantity ofthe second pattern portion, namely, processing up to processes 2001-2003is the same as for the construction of the model described earlier inthis document.

In process 2004, focus value F is calculated by assigning EW1 and EW2,the dimensional characteristic quantities that were calculated inprocesses 2002 and 2003 (in this case, x=EW1−EW2), to theabove-described model which represents the relationship between edgewidths and focal deviations.

In process 2005, exposure level E is calculated by assigning LW1, thedimensional characteristic quantity that was calculated in process 2002(in this case, x=LW1), to the above-described model which represents therelationship between pattern widths and exposure levels.

In process 2006, the calculated values of ΔE=E−E0 and ΔF=F−F0 are fedback as the amounts of correction of the exposure conditions. In thisway, the optimal conditions are always maintained in this embodiment ofthe invention.

(5) Configuration Supplied by This Embodiment

The more specific configuration supplied by the above-describedembodiment is described below.

A process conditions change monitoring system comprising

an image detection means (unit) for obtaining electron beam images ofresist patterns (this process corresponds to electron beam acquisition11),

a dimensional characteristic quantity detection means (unit) foracquiring the respective dimensional characteristic quantities of afirst pattern portion and a second pattern portion differing from oneanother in terms of the tendency of the changes in edge widths and/orpattern widths and other dimensional characteristic quantities againstchanges in exposure conditions (this process corresponds to calculation12 of the dimensional characteristic quantities (LW1 and LW2) of thefirst pattern portion and to calculation 13 of the dimensionalcharacteristic quantity (EW2) of the second pattern portion),

a means of saving the models for establishing logical linking betweenexposure conditions and dimensional characteristic quantities, and

a means (unit) for calculating changes in exposure conditions byapplying, to said models, those dimensional characteristic quantities ofsaid first pattern portion and said second pattern portion that havebeen acquired by said dimensional characteristic quantity detectionmeans (this process corresponds to calculation 14 of ΔF by theapplication of models to EW1 and EW2 and to calculation 15 of ΔE by theapplication of a model to LW1),

and further equipped with

a means (unit) for providing exposure conditions correction based on thechanges in exposure conditions that have been calculated by saidcalculation means (this process corresponds to ΔE, ΔF data transmission16).

A semiconductor substrate manufacturing system intended to change thefocus value, one of exposure conditions, by use of electron beam imagesof resist patterns, wherein the semiconductor substrate manufacturingsystem has an image detection means for obtaining electron beam imagesof said resist patterns, a means by which the focal deviation tolerancesat which the rate of change of the edge width of the particular resistpattern against changes in focus value is maintained at or below a fixedvalue are calculated from the two pattern portions of said electron beamimages, a means (unit) for providing exposure within the focal deviationtolerances that have been calculated by said calculation means (thisexposure process corresponds to exposure 17).

A process conditions change monitoring method for monitoring changes inexposure conditions by use of electron beam images of resist patternsduring lithography, wherein said monitoring method is characterized inthat: images for obtaining electron beam images of said resist patternsare detected, the dimensional characteristic quantities of the resistpatterns, including the respective edge widths and pattern widths, arecalculated from the electron beam images, and models for establishinglogical linking between exposure conditions are provided; changes fromthe optimal exposure conditions are calculated by first acquiringelectron beam images of a first pattern portion and a second patternportion different from one another in the tendency of the changes indimensional characteristic quantities against changes in exposureconditions, by said image detection during exposure conditions changemonitoring, then calculating the respective dimensional characteristicquantities of the first pattern portion and the second pattern portionby said dimensional characteristic quantity calculation, and calculatingactual changes in exposure conditions through applying the correspondingcharacteristic quantities to the models which establish logical linkingbetween said exposure conditions and said dimensional characteristicquantities, and; the exposure conditions are corrected according to theparticular calculation results.

(6) Effects of This Embodiment

According to this embodiment, the three problems described in “Problemsto be Solved by the Invention” are solved. First, how to solve the firstproblem, namely, the inability to detect changes in focus, is described.According to this embodiment, changes in focus can be reliably detectedby monitoring edge widths EW1 and EW2. Next, with reference to thesecond problem (namely, the feedback of changes in focus), according tothis embodiment, it is possible to not only detect focal deviations, butalso calculate them accurately, by applying edge widths EW1 and EW2 tospecial models. With reference to the third problem (namely, theinability to quantitatively determine changes in process conditions),according to this embodiment, it is possible to calculate accuratedeviations by applying edge widths EW1 and EW2 to the above-mentionedmodels, to calculate accurate changes in exposure level by applying linewidth LW1 to a special model, and even to prevent the occurrence ofdefects in the shape of the film pattern existing after etching.

Also, despite the above-described effects produced from the firstembodiment of the present invention, the time required for the executionof the series of operations shown as processes 2002 to 2005 in FIG. 1 isalmost the same as the time required for dimensional measurement withCD-SEM during conventional lithography. Therefore, there is theadvantage that process throughput does not decrease.

In addition, although, during conventional conditions establishingoperations, the determination of the optimal exposure conditions andprocess window data depends on the subject of the operator, the presentinvention has the advantage that since the determination is based onmodels, such data can be determined not only accurately, but also alwayswith equal accuracy.

(7) Second Preferred Mode of Embodiment

The second preferred embodiment of the present invention is shown inFIG. 10.

Processes 11 to 15 in FIG. 10 are the same as those of the firstembodiment shown in FIG. 1. The same number is assigned to each processin the same mode of embodiment, and the description of FIG. 1 applies byanalogy. Processes 40, 41, and 42 are added to the configuration shownin FIG. 1. The first mode of embodiment is based on the assumption thatboth the exposure level and focus slowly change with time, and isintended to control processes so that the process window data range isnot overstepped. However, if any significant changes in processconditions occur abruptly, this may result in feedback data errors(errors in ΔE, ΔF) since the models used to calculate ΔE and ΔF can beexpressed as the models having mutually independent parameters inprocess windows as described above. Under this second embodiment, inprocess 40, the value of ΔE is checked and if this value is outside itsreference (process window), control is moved to the sequence forcalculating ΔE and ΔF once again. In process 41, ΔF is recalculated byapplying EW1 and EW2 to another model which calculates ΔF with ΔE takeninto consideration. In process 42, ΔE is recalculated by applying LW1 toanother model which calculates ΔE with ΔF taken into consideration.

This embodiment can be implemented either by creating beforehand themodel representing the relationship between focus and edge widths (EW1,EW2) for each exposure level, and the model representing therelationship between exposure level and line width (LW1) for each focusvalue, by, instead of assigning the above-mentioned models as relationalexpressions and calculating the optimal exposure conditions, providing alookup table 31 in which EW1, LW1, and EW2 have been defined for eachset of exposure conditions as shown in FIG. 11 and searching for theexposure conditions (ΔE, ΔF) that EW1, LW1, and EW2 best match, or byproviding both the above-mentioned models and lookup table and referringto the lookup table only if the process window is overstepped.

According to this embodiment, it is possible to realize process controlthat enables the proper response even in the event of abrupt significantchanges in process conditions.

(8) Third Mode of Embodiment

The third preferred embodiment of the present invention is shown in FIG.12.

Processes 11 to 15 in FIG. 12 are the same as those of the firstembodiment shown in FIG. 1. The same number is assigned to each processin the same mode of embodiment, and the description of FIG. 1 applies byanalogy. After ΔF calculation in process 15, the calculated ΔE and ΔFdata is not fed back as it is. Instead, old ΔE and ΔF data is referredto in process 51 and the final ΔE1 and ΔF1 quantities are determined inprocess 52. History database 303, for example, contains the ΔE and ΔFdata relating to several old product lots, and the final ΔE1 and ΔF1quantities are determined by assigning straight lines to the data withinthe history database as shown in FIG. 12(b).

Even when the same exposure level and the same focus value are given,resist patterns completely equal in microscopic terms will not be alwaysformed. In addition, if even slight differences in the conditionsestablished to acquire images with CD-SEM occur or if dimensionalcharacteristic quantity calculation errors occur, the ΔE and ΔF datacalculated from individual inspection targets will include certainerrors. Also, since changes in focus are drift-like changes rather thanabrupt changes, this embodiment enables stable process control incomparison with the determination of feedback quantities from a singleset of results.

Of course, the history database does not always need to be presentinside CD-SEM, and it can exist in other memory units present on aparticular network. Also, although several old product lots of data isused as history data in the figure, the term “several old product lotsof data” merely refers to an example and the second embodiment is notlimited to this example.

(9) Other Information

Although it has up to now been described in this document that both thefirst pattern portion and the second pattern portion are present on oneimage, when suitable patterns are not adjacently present, even ifindependent images are acquired, there will be no effects onperformance.

Also, special marks for monitoring the exposure conditions can beprovided on the wafer. In this case, however, it is desirable that amasked pattern with critical dimensions and a non-masked pattern withcritical dimensions should be arranged for the first pattern portion andthe second pattern portion, respectively, on one image.

An example of pattern arrangement is shown in FIG. 13. FIG. 13(a) showsan image of a binary mask pattern, wherein white and black denote atransmitting portion and a shielding portion, respectively. Since theleft and right patterns in FIG. 13(a) are patterns whose transmittingportion and shielding portions are reversed, both the masked pattern(left) and the non-masked pattern (right) can be formed. The acquisitionof an after-development electron beam image enables the obtainment of animage which represents bright edge portions and dark flat portions asshown in FIG. 13(b). In FIG. 13(b), the E-F cross section is taken asthe first pattern, and the G-H cross section is taken as the secondpattern. The cross-sectional shapes of sections E-F and G-H are shown inFIG. 14. A conceptual diagram of after-development patterns is shown asFIG. 14(b). For example, when attention is drawn to the pattern near thecenter and the edge width (EW1) of the masked pattern, the edge width(EW2) of the non-masked pattern, and the line width (LW1) of the maskedpattern are measured from electron beam images, it will be possible toobtain the same effects as those of the patterns shown in FIGS. 4 and 5.When, similarly to the arrangement of the patterns used in FIG. 14(b),one pattern is surrounded by a multitude of patterns of the same shape,it will also be valid to minimize measurement errors by measuring theedge widths (EW1 and EW2) of the multiple patterns of the same shape andthe line width (LW1) of the center pattern and using their averagevalues.

Yet another example is shown in FIG. 15. FIG. 15(a) shows an image of abinary mask pattern, wherein white and black denote a transmittingportion and a shielding portion, respectively. A conceptual diagram ofafter-development patterns is shown as FIG. 15(b). The center holepattern corresponds to the non-masked pattern (first pattern portion),and the outer wall portion corresponds to the masked pattern (secondpattern portion). FIG. 16(a) shows an electron beam image of thispattern, wherein the image is bright at its edge portions and dark atits flat portion. The cross-sectional shape of this image is shown inFIG. 16(b). When the edge width (EW1) of the outer wall and the edgewidth (EW2) of the inner wall are measured from the electron beam imageof FIG. 16(a), it will be possible to obtain the same effects as thoseof the patterns shown in FIGS. 4 and 5.

Important is that the first pattern portion and the second patternportion should differ in behavior with respect to focus, and theircombination does not always need to be such that the behaviors of bothpatterns are as shown in FIGS. 6(a) and (b). Also, although theexpression for calculating the focus value from EW1−EW2 is used as thefocus value calculation model (see numerical expression 1), thisexpression has been adopted because it is a relational expressionsuitable for such behavior as shown in FIGS. 6(a) and (b). If thepattern to be used differs, therefore, another relational expressioncan, of, course, be used. In addition, three or more patterns, not twopatterns, can be used.

Furthermore, although, up to now, the image acquisition positions on thewafer to be inspected have not been described in this document, whenthis embodiment is to be put into actual operation, it is desirable thatΔE and ΔF should be determined as exposure conditions feedbackquantities by acquiring images on a plurality of positions on the waferand synthetically judging the characteristic quantities obtained fromthe images.

Furthermore, for more accurate measurement results on edge width, theimages acquired by tilting the stage or the beam can also be used.

The following process conditions change monitoring systems and methodsare supplied as the systems and methods that use electron beams:

A process conditions change monitoring system and method for monitoringchanges in exposure conditions by use of electron beam images of resistpatterns during lithography, wherein said monitoring system and methodis characterized in that: an image detection means for obtainingelectron beam images of said resist patterns, a means for calculatingthe dimensional characteristic quantities of the resist patterns,including the respective edge widths and pattern widths, from theelectron beam images, and models for establishing logical linkingbetween exposure conditions are provided; changes from the optimalexposure conditions are calculated by first acquiring electron beamimages of a first pattern portion and a second pattern portion differentfrom one another in the tendency of the changes in dimensionalcharacteristic quantities against changes in exposure conditions, bysaid image detection means during exposure conditions change monitoring,then calculating the respective dimensional characteristic quantities ofthe first pattern portion and the second pattern portion by saiddimensional characteristic quantity calculation means, and calculatingactual changes in exposure conditions through applying the correspondingcharacteristic quantities to the models which establish logical linkingbetween said exposure conditions and said dimensional characteristicquantities, and; the exposure conditions are corrected according to theparticular calculation results.

A process conditions change monitoring system and method for monitoringchanges in exposure conditions by use of electron beam images of resistpatterns during lithography, wherein said monitoring system and methodis characterized in that: an image detection means for obtainingelectron beam images of said resist patterns, a means for calculatingthe dimensional characteristic quantities of the resist patterns,including the respective edge widths and pattern widths, from theelectron beam images, and models for establishing logical linkingbetween exposure conditions are provided; changes from the optimalexposure energy level are calculated by first acquiring electron beamimages of a first pattern portion and a second pattern portion differentfrom one another in the tendency of the changes in edge width againstchanges in exposure focus, by said image detection means during exposureconditions change monitoring, then calculating the respectivedimensional characteristic quantities of the first pattern portion andthe second pattern portion by said dimensional characteristic quantitycalculation means, and calculating actual changes in the focus value andenergy level existing during exposure through applying the correspondingcharacteristic quantities to the models which establish logical linkingbetween said exposure conditions and said dimensional characteristicquantities, and; the exposure conditions are corrected according to theparticular calculation results.

A process conditions change monitoring system and method characterizedin that said first pattern portion is a pattern disposed so as toincrease in edge width when the focus value deviates in a plusdirection, and in that said second pattern portion is a pattern disposedso as to increase in edge width when the focus value deviates in a minusdirection.

A process conditions change monitoring system and method characterizedin that a masked pattern with about critical dimensions and a non-maskedpattern with about critical dimensions are used as said first patternportion and second pattern portion, respectively.

A process conditions change monitoring system and method characterizedin that different places within one image are used as said first patternportion and second pattern portion.

A process conditions change monitoring system and method characterizedin that said models for establishing logical linking between saidexposure conditions and dimensional characteristic quantities are forstoring into memory the relationship between changes in the edgewidth(s) and focus value(s) of said first and/or second pattern or therelationship between changes in the pattern width(s) and energy level(s)of said first and/or second pattern.

A process conditions change monitoring system and method characterizedin that said models for establishing logical linking between saidexposure conditions and dimensional characteristic quantities are fordetermining F from EW1 and EW2, wherein the focus value, the edge widthcalculated from the first pattern portion, and the edge width calculatedfrom the second pattern portion are taken as F, EW1, and EW2,respectively; in other words, for determining actual changes in thefocus value when F=f (EW1, EW2).

A process conditions change monitoring system and method characterizedin that said models for establishing logical linking between saidexposure conditions and dimensional characteristic quantities are tablesin which the dimensional characteristic quantities against variousexposure conditions are defined for said first pattern portion andsecond pattern portion each.

A process conditions change monitoring system and method characterizedin that when said models for establishing logical linking between saidexposure conditions and dimensional characteristic quantities areconstructed, electron beam images against various changes in focus valueand in exposure energy level are acquired using the exposure test piecesthat shift the focus value and exposure energy level of the exposureunit in steps, and calculation results on the respective dimensionalcharacteristic quantities are incorporated into the construction of themodels.

A process conditions change monitoring system and method for monitoringchanges in exposure conditions by use of electron beam images of resistpatterns during lithography, wherein said monitoring system and methodis characterized in that an image detection means for obtaining electronbeam images of said resist patterns, a means for calculating thedimensional characteristic quantities of the resist patterns, includingthe respective edge widths and pattern widths, from the electron beamimages, and models for establishing logical linking between exposureconditions are provided and in that a function is further provided thatautomatically determines process window data, namely, focal deviationtolerances and exposure energy level error tolerances, from therelationships between edge width and focal deviations and therelationship between pattern width and exposure energy level.

The meanings of the signs assigned to the focus value of the exposureunit may vary from manufacturer to manufacturer. In the presentinvention, however, the definitions used in FIG. 21 are used.

According to the present invention, changes in focus can be detected. Itis also possible to supply the process conditions change monitoringsystem and methods that enable not only the detection of changes inexposure level, but also output of information that quantitativelyrepresents changes in process conditions, namely, accurate changes inexposure level and in focus. As a result, it is possible to detect suchdefects in stereographic shape due to focal deviations as have beenoverlooked during conventional measurement of dimensions, and thus toavoid defects in the formation of a non-reproducible film pattern afteretching. Furthermore, although the determination of the optimal exposureconditions and process window data during conventional conditionsestablishing operations depends on the subject of the operator, thepresent invention enables such data to be determined not onlyaccurately, but also always with equal accuracy, since the determinationis based on models.

What is claimed is:
 1. A process conditions change monitoring system ofa scanning-type electronic microscope equipped with a monitoring unitfor monitoring changes in exposure conditions by use of electron beamimages of a resist pattern, comprising: an image detection unit forobtaining electron beam images of said resist pattern; a dimensionalcharacteristic quantity detection means for detecting the respectivedimensional characteristic quantities of a first pattern portion and asecond pattern portion, which are different from one another in thetendency of the changes in dimensional characteristic quantities,showing the edge widths of the pattern, against changes in exposureconditions; a memory storing models for establishing logical linkingbetween exposure conditions and dimensional characteristic quantities;and a calculating unit calculating changes in exposure conditionsrelating to the focus of said scanning-type electronic microscope byapplying, to said models, those dimensional characteristic quantities ofsaid first pattern portion and said second pattern portion that havebeen acquired by said dimensional characteristic quantity detectionmeans.
 2. The process conditions change monitoring system of thescanning-type electronic microscope according to claim 1, furthercomprising a correcting unit for correcting exposure condition accordingto the changes in exposure conditions that have been calculated by saidcalculating unit.
 3. A process conditions change monitoring system of ascanning-type electronic microscope equipped with a monitoring unit formonitoring changes in exposure conditions relating to focus value, byuse of electron beam image of a resist pattern, comprising: an imagedetection unit for obtaining electron beam images of said resistpattern; a dimensional characteristic quantity detection means fordetecting the respective dimensional characteristic quantities of theedge widths of a first pattern portion and a second pattern portion,which are different from one another in the tendency of the changes inthe dimensional characteristic quantities of the edge widths of theresist pattern, against changes in focus value; a memory storing modelsfor establishing logical linking between focus value and dimensionalcharacteristic quantities; and a calculating unit for calculatingchanges in focus value by applying, to said models, those dimensionalcharacteristic quantities of said first pattern portion and said secondpattern portion that have been acquired by said dimensionalcharacteristic quantity detection means.
 4. The process conditionschange monitoring system of the scanning-type electronic microscopeaccording to claim 3, wherein said exposure conditions include exposurelevels, in that said models establish logical linking between exposurelevels and dimensional characteristic quantities, and wherein saidcalculation unit also calculates changes in exposure level by applyingto the corresponding models the dimensional characteristic quantities,including the pattern widths of said first pattern portion and saidsecond pattern portion that have been acquired by said detection unit.5. The process conditions change monitoring system of the scanning-typeelectronic microscope according to claims 3 or 4 above, furthercomprising correcting the focus value according to the changes in thefocus value that have been calculated by said calculating unit.
 6. Theprocess conditions change monitoring system of the scanning-typeelectronic microscope according to claims 3 or 4 above, wherein saidcalculating unit calculates tolerances on focus value deviations and onexposure energy changes.